What is the most expensive ad?

I'm curious, what exactly constitutes the most expensive advertisement in today's market? Is it measured by the sheer dollar amount invested, or is there more to it than meets the eye? Do these ads often utilize cutting-edge technology or unique marketing strategies? Are they targeted towards a niche audience or do they aim for mass appeal? And finally, what kind of impact does such a lavish expenditure have on the overall success of a product or brand?